Imaging lens

ABSTRACT

An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; and a fifth lens having negative refractive power, arranged in this order from an object side to an image plane side. The first lens is formed in a shape so that an object side surface thereof has a positive curvature radius. The second lens is formed in a shape so that an object side surface thereof and an image plane side surface thereof have positive curvature radii. The first lens, the third lens, and the second lens have specific Abbe&#39;s numbers. The third lens has a specific focal length so that a specific conditional expression is satisfied. The second lens, the third lens, and the fourth lens are arranged so that a specific conditional expression is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of a reissue application Ser. No.14/824,208, filed on Aug. 12, 2015, pending, of U.S. Pat. No. 8,879,167,issued on Nov. 4, 2014.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an opticalimage on an imaging element such as a CCD sensor and a CMOS sensor.Particularly, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a cellular phone, adigital still camera, a portable information terminal, a securitycamera, an onboard camera, and a network camera.

Performances of a camera mounted in a cellular phone have been improvedevery year, and there is even a camera having optical performancescomparable to those of a digital still camera. The resolution of animaging element that used to be several hundred thousand pixels has beenimproved to several megapixels, and the resolution of a camera has beendramatically improved. An imaging lens for mounting in such camera needsto not only have a small size, but also have resolution comparable tothat of a high-resolution imaging element, i.e., ability tosatisfactorily correct aberrations.

Conventionally, in order to attain both sufficient optical performancesand miniaturization, it is typical to adopt an imaging lens having twoor three-lens configuration. However, optical performances required forsuch a high-resolution imaging element have been increased each year, sothat it is difficult to sufficiently correct aberrations anymore.Further, it is difficult to meet those optical performance requirementswith such a two- or three-lens configuration. For this reason, a four-or five-lens configuration has been studied and practically applied inrecent years.

Among them, since a five-lens configuration has high flexibility indesigning, it is expected to be a lens configuration to be applied to anext generation imaging lens. For example, an imaging lens described inPatent Reference includes a first lens that is convex on an object-sidesurface thereof and is positive; a second lens that has a shape of anegative meniscus lens directing a concave surface thereof to an imageplane side; a third lens that has a shape of a positive meniscus lensdirecting a convex surface thereof to the image plane side; a fourthlens that has aspheric shapes on both surfaces thereof, is concave on animage plane-side surface thereof near an optical axis, and is negative;and a fifth lens that has aspheric shapes on both surfaces thereof andis positive or negative, arranged in this order from the object side. Inaddition, there are limitations in a lower limit of Abbe's number of thefirst lens and an upper limit of Abbe's number of the second and thefourth lenses. With the lens configuration like this, according to theimaging lens, it is possible to satisfactorily correct an axialchromatic aberration and a chromatic aberration of magnification.

Patent Reference: Japanese Patent Application Publication No.2007-264180

According to the imaging lens described in Patent Reference, it ispossible to obtain relatively satisfactory aberrations. However, sincethe total length of the lens system is long, it is difficult to attainboth miniaturization of the imaging lens and satisfactory aberrationcorrection. Here, such challenge of attaining both miniaturization andsatisfactory aberration correction is not specific to the imaging lensfor mounting in a cellular phone, but common among imaging lenses formounting in relatively small cameras such as digital still cameras,portable information terminals, security cameras, onboard cameras, andnetwork cameras.

In view of the above-described problems, an object of the presentinvention is to provide an imaging lens that can satisfactorily correctaberrations in spite of the small size thereof.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to an aspectof the present invention, an imaging lens includes a first lens havingpositive refractive power; a second lens having negative refractivepower; a third lens having positive refractive power; a fourth lenshaving negative refractive power; and a fifth lens having negativerefractive power, arranged in the order from an object side to an imageplane side. The first lens is formed in a shape so that a curvatureradius of an object-side surface thereof is positive and the second lensis formed in a shape so that a curvature radius of an object-sidesurface thereof and a curvature radius of an image plane-side surfacethereof are both positive. The third lens is formed in a shape so that acurvature radius of an object-side surface thereof is positive, and thefifth lens is formed in a shape so that a curvature radius of anobject-side surface thereof and a curvature radius of an imageplane-side surface thereof are both positive. According to theconfiguration, the imaging lens of the invention satisfies a conditionthat an Abbe's number of each lens from the first lens, and the thirdlens to the fifth lens is greater than 45 and an Abbe's number of thesecond lens is less than 35.

In order to enhance resolution of an imaging lens so as to be compatiblewith a high-resolution imaging element available in these years, it isnecessary to satisfactorily correct aberrations, especially chromaticaberrations. According to a configuration of the imaging lens of theinvention, the Abbe's number of the first lens is greater than 45 andthe Abbe's number of the second lens is less than 35, and the first lensand the second lens are formed by combining a low-dispersion materialand a high-dispersion material. In addition, each lens from the thirdlens to the fifth lens has the Abbe's number greater than 45 and isformed of a low-dispersion material. Therefore, a chromatic aberrationoccurred in the first lens is corrected by the second lens and at thesame time, satisfactorily corrected through each lens from the thirdlens to the fifth lens.

Here, according to the imaging lens having the above-describedconfiguration, preferably, each lens of the first lens and lenses fromthe third to the fifth lenses has the same Abbe's number and is made ofthe same material. With this configuration, it is possible to suitablyattain productivity improvement and manufacturing cost reduction of theimaging lens. In addition, forming each lens from the first lens to thefifth lens from a plastic material, it is possible to further attainproductivity improvement and manufacturing cost reduction.

When the first lens has a focal length f1, the second lens has a focallength f2, the third lens has a focal length f3, the fourth lens has afocal length f4, and the fifth lens has a focal length f5, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expressions (1) and (2):

f1<f3 and |f2|<f3  (1)

f3<|f4| and |f2|<|f5|  (2)

When the imaging lens satisfies the conditional expressions (1) and (2),it is possible to satisfactorily correct aberrations while attainingminiaturization of the imaging lens. When the imaging lens satisfies theconditional expressions (1) and (2), the first lens and the second lens,which are arranged on the object side, have stronger refractive powerthan other three lenses. With the configuration, it is possible toshorten a total optical length of the imaging lens while securingcertain angle of view, and it is possible to suitably attainminiaturization of the imaging lens. In addition, according to theinvention, each lens from the third lens to the fifth lens hasrelatively weak refractive power. Aberrations occurred in the first lensand the second lens, which have strong refractive powers, are suitablycorrected through each lens from the third lens to the fifth lens, whichhave weak refractive powers.

In the imaging lens having the above-described configuration, the fourthlens is preferably formed in a shape so that a curvature radius of anobject-side surface thereof and a curvature radius of an imageplane-side surface thereof are both negative.

As described above, the second lens is formed in a shape so that acurvature radius of the object-side surface thereof and a curvatureradius of the image plane-side surface thereof are both positive, i.e. ashape of a meniscus lens directing a convex surface thereof to theobject side. Furthermore, the fourth lens is formed in a shape so that acurvature radius of the object-side surface thereof and a curvatureradius of the image plane-side surface thereof are both negative, i.e. ashape of a meniscus lens directing a concave surface thereof to theobject side. Therefore, the second lens and the fourth lens are arrangeddisposing their concave surfaces to the third lens. With thisconfiguration, aberrations occurred in the first lens are suitablycorrected also by the negative-positive-negative refractive powerarrangement of the lenses from the second to the fourth lenses and theshapes of the respective lenses of the second lens and the fourth lens.

When the whole lens system has a focal length f and the second lens hasthe focal length f2, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(3):

−1.8<f2/f<−0.8  (3)

When the imaging lens satisfies the conditional expression (3), it ispossible to restrain a chromatic aberration and a field curvature withinpreferred ranges. When the value exceeds the upper limit “−0.8”, sincethe second lens has strong refractive power in relative to the wholelens system, an axial chromatic aberration is excessively corrected (afocal position at a short wavelength moves towards the image plane sidein relative to a focal position at a reference wavelength), and at thesame time, an off-axis chromatic aberration of magnification isexcessively corrected (an image-forming point at a short wavelengthmoves in a direction to be away from the optical axis in relative to animage-forming point at a reference wavelength). In addition, animage-forming surface curves to the image plane side and it is difficultto obtain satisfactory image-forming performance. On the other hand,when the value is below the lower limit “−1.8”, the second lens has weakrefractive power in relative to the whole lens system, so that an axialchromatic aberration is insufficiently corrected (a focal position at ashort wavelength moves towards the object side in relative to a focalposition at a reference wavelength) and an off-axis chromatic aberrationof magnification is insufficiently corrected (an image-forming point ata short wavelength moves in a direction to approach the optical axis inrelative to an image-forming point at a reference wavelength). Moreover,an image-forming surface curves to the object side, so that it isdifficult to obtain satisfactory image-forming performance also in thiscase.

When the first lens has the focal length f1 and the second lens has thefocal length f2, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(4):

−1.0<f1/f2<−0.4  (4)

When the imaging lens satisfies the conditional expression (4), it ispossible to restrain an astigmatism, a field curvature, and a chromaticaberration within preferred ranges in a well-balanced manner, whilerestraining Petzval sum near zero. When the value exceeds the upperlimit “−0.4”, the first lens has strong refractive power in relative tothe second lens, an axial and an off-axis chromatic aberrations areinsufficiently corrected. As for the astigmatism, a tangential imagesurface tilts to the object side and an astigmatic difference increases.For this reason, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limit“−1.0”, the first lens has weak refractive power in relative to thesecond lens, so that negative refractive power is strong and an axialand an off-axial chromatic aberrations are excessively corrected. Inaddition, an image-forming surface curves to the image plane side. Asfor the astigmatism, a tangential image surface tilts to an image planeside and the astigmatic difference increases. Therefore, also in thiscase, it is difficult to obtain satisfactory image-forming performance.

When a curvature radius of the object-side surface of the second lens isR2 f and a curvature radius of the image plane-side surface thereof isR2 r, the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (5):

1.5<R2f/R2r<6.0  (5)

When the imaging lens satisfies the conditional expression (5), it ispossible to restrain a coma aberration, a field curvature, and achromatic aberration within preferred ranges, respectively. When thevalue exceeds the upper limit “6.0”, the second lens has relativelystrong refractive power, an outer coma aberration of an off-axis lightbeam increases, and an axial and an off-axis chromatic aberrations areexcessively corrected. In addition, since an image-forming surfacecurves to the image plane side, it is difficult to obtain satisfactoryimage forming performance. On the other hand, when the value is belowthe lower limit “1.5”, the second lens has relatively weak refractivepower, and the axial and the off-axis chromatic aberrations areinsufficiently corrected. Moreover, the image forming surface curves tothe object side, and also in this case, it is difficult to obtainsatisfactory image forming performance.

When the whole lens system has the focal length f and the third lens hasthe focal length f3, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(6):

5.0<f3/f<20.0  (6)

According to the imaging lens of the invention, the third lens mainlyserves for correcting aberrations. When the imaging lens satisfies theconditional expression (6), it is possible to more satisfactorilycorrect aberrations while attaining miniaturization of the imaging lens.When the value exceeds the upper limit “20.0”, since the third lens hasweak refractive power in relative to the whole lens system, it isdifficult to attain miniaturization of the imaging lens. Here, when thethird lens has weak refractive power, it is possible to attainminiaturization of the imaging lens by increasing the refractive powerof the fourth lens or the fifth lens. In this case, however, it isdifficult to correct aberrations (especially coma aberration), and it isdifficult to obtain satisfactory image forming performance. On the otherhand, when the value is below the lower limit “5.0”, although it isadvantageous for attaining miniaturization of the imaging lens, the comaaberration increases and the astigmatic difference also increases.Therefore, also in this case, it is difficult to obtain satisfactoryimage forming performance.

When the maximum effective diameter of the object-side surface of thethird lens is Φ_(3A), the maximum effective diameter of the imageplane-side surface thereof is Φ_(3B), the maximum effective diameter ofthe object-side surface of the fourth lens is Φ_(4A), the maximumeffective diameter of the image plane-side surface thereof is Φ_(4B),and the maximum absolute value of a sag (sagittal height) at up to 70%of the maximum effective diameters Φ_(3A) to Φ_(4B) is Z_(0.7), theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (7):

Z _(0.7) /f<0.1  (7)

Therefore, restraining the maximum sag within certain range, the thirdlens and the fourth lens are formed in shapes that have substantiallyuniform thickness in the optical axis direction and are less curved.With such shapes of the third and the fourth lenses, generation ofcomplicated aberrations is restrained and aberrations occurred in thefirst and the second lenses are satisfactorily corrected. Furthermore,sensitivity to deterioration of the image-forming performance due todecentering (axial displacement), tilting, or the like uponmanufacturing the imaging lens, i.e., so-called “production errorsensitivity” decreases. In addition, because of the substantiallyuniform thickness in the optical axis direction, fabrication propertiesupon production are improved and manufacturing cost of the imaging lensis restrained. Here, “sag” means, in each surface, a distance in adirection parallel to the optical axis from a tangential plane that isorthogonal to the optical axis to the surface.

When the whole lens system has the focal length f and a composite focallength of the third lens and the fourth lens is f34, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (8):

5.0<f34/f<25.0  (8)

Restraining a ratio of the composite focal length of the third lens andthe fourth lens to the focal length of the whole lens system within therange defined by the conditional expression (8), it is possible to moresatisfactorily correct aberrations. When the value exceeds the upperlimit “25.0”, the composite refractive power of the third lens and thefourth lens is relatively weak and it is difficult to restrainaberrations within preferred ranges in a well-balanced manner. On theother hand, when the value is below the lower limit “5.0”, compositerefractive power of the third lens and the fourth lens is relativelystrong, so although it is advantageous for correction of a distortion,the astigmatic difference increases. Therefore it is difficult to obtainsatisfactory image-forming performance.

When a distance on the optical axis from the image plane-side surface ofthe second lens to the object-side surface of the third lens is dA and adistance on the optical axis from the image plane-side surface of thethird lens to the object-side surface of the fourth lens is dB, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (9):

0.3<dA/dB<1.5  (9)

In case of an imaging element such as a CCD sensor and a CMOS sensor,there is a limited range in an angle to take an incident light beam dueto its structure. When an emitting angle of an off-axis light beam isoutside the limited range above, it is difficult for a sensor to taketherein light beams outside the limited range, which results in aso-called shading phenomenon. More specifically, an image obtainedthrough the imaging lens has a dark periphery that is darker than thecenter part.

When the imaging lens satisfies the conditional expression (9), it ispossible to keep the maximum emitting angle of an off-axis light beamsmall, while attaining miniaturization of the imaging lens. When thevalue exceeds the upper limit “1.5”, although it is easy to keep themaximum emitting angle of the off-axis light beam small, it is difficultto attain miniaturization of the imaging lens. On the other hand, whenthe value is below the lower limit “0.3”, although it is advantageousfor miniaturization of the imaging lens, a chromatic aberration isinsufficiently corrected and it is difficult to obtain satisfactoryimage-forming performance. In addition, since the maximum emitting angleof an off-axis light beam is large, the shading phenomenon easilyoccurs.

According to the imaging lens of the invention, it is possible to attainboth miniaturization and satisfactory aberration correction of theimaging lens and provide a small-sized imaging lens with satisfactorilycorrected aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a schematic configuration of animaging lens of Numerical Data Example 1 according to an embodiment ofthe invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 is a sectional view showing a schematic configuration of animaging lens of Numerical Data Example 2 according to the embodiment ofthe invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 is a sectional view showing a schematic configuration of animaging lens of Numerical Data Example 3 according to the embodiment ofthe invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 is a sectional view showing a schematic configuration of animaging lens of Numerical Data Example 4 according to an embodiment ofthe invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 is a sectional view showing a schematic configuration of animaging lens of Numerical Data Example 5 according to the embodiment ofthe invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13; and

FIG. 15 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, and 13 are schematic sectional views of imaginglenses in Numerical Data Examples 1 to 5 according to the embodiment,respectively. Since a basic lens configuration is the same among thoseNumerical Data Examples, the lens configuration of the embodiment willbe described with reference to the schematic sectional view of NumericalData Example 1.

As shown in FIG. 1, the imaging lens of the embodiment includes a firstlens L1 having positive refractive power, a second lens L2 havingnegative refractive power, a third lens L3 having positive refractivepower, a fourth lens L4 having negative refractive power, and a fifthlens L5 having negative refractive power, arranged in the order from anobject side to an image plane side. A filter 10 such as an infraredcut-off filter or a cover glass may be provided between the fifth lensL5 and an image plane IM. The filter 10 may be optionally omitted. Here,according to the imaging lens of this embodiment, there is provided anaperture stop on an object-side surface of the first lens L1.

According to the imaging lens of the embodiment, Abbe's numbers νd1 andνd3 to νd5 of the first lens and the lenses from the third lens L3 tothe fifth lens L5 are respectively larger than 45, and an Abbe's numberνd2 of the second lens L2 is smaller than 35. More specifically, thefirst lens L1 and the second lens L2 are made from a combination oflow-dispersion material and a high-dispersion material, and each of thelenses from the third lens L3 to the fifth lens L5 is made of alow-dispersion material. With this arrangement of the Abbe's numbers, achromatic aberration occurred in the first lens L1 is corrected by thesecond lens L2 and also satisfactorily corrected through each of thelenses from the third lens L3 to the fifth lens L5. In addition, sincefour of the five lenses from the first lens L1 to the fifth lens L5 aremade of low-dispersion materials, generation of a chromatic aberrationitself is suitably restrained. Here, more specifically, the Abbe'snumbers νd1 to νd5 of the lenses from the first lens L1 to the fifthlens L5 are preferably restrained within ranges defined by the followingconditional expressions, respectively. The imaging lenses of NumericalData Examples 1 to 5 satisfy the following conditional expressions:

45<νd1<85

νd2<35

45<νd3<85

45<νd4<85

45<νd5<85

According to the imaging lenses in Numerical Data Examples 1 to 5 ofthis embodiment, the first lens L1 and each of the lenses from the thirdlens L3 to the fifth lens L5 have the same Abbe's number, and each lensis made of a same plastic material. For this reason, it is possible tosuitably attain productivity improvement and manufacturing costreduction of the imaging lens.

Furthermore, each of the lenses from the first lens L1 to the fifth lensL5 satisfies the following conditional expressions (1) and (2):

f1<f3 and |f2|<f3  (1)

f3<|f4| and |f2|<|f5|  (2)

In the above conditional expressions:f1: Focal length of a first lens L1f2: Focal length of a second lens L2f3: Focal length of a third lens L3f4: Focal length of a fourth lens L4f5: Focal length of a fifth lens L5

As described above, according to the imaging lens of this embodiment,the first lens L1 and the second lens L2, which are arranged on theobject side in the imaging lens, have refractive powers that arestronger than those of other three lenses. Because of this, it ispossible to attain miniaturization of the imaging lens and also suitablycorrect aberrations occurred in the first lens L1 and the second lens L2through the respective lenses from the third lens L3 to the fifth lensL5, which have weak refractive powers.

According to the imaging lens having the above-described configuration,the first lens L1 is formed in a shape so that a curvature radius of anobject-side surface thereof R1 and a curvature radius of an imageplane-side surface thereof R2 are both positive, i.e. a shape of ameniscus lens directing a convex surface thereof to the object side nearan optical axis X. Here, the shape of the first lens L1 is not limitedto a shape of the meniscus lens directing a convex surface thereof tothe object side near the optical axis X, and can be any as long as thecurvature radius of the object-side surface thereof R1 is positive. Morespecifically, as a shape of the first lens L1, it is possible to form ina shape so that the curvature radius R1 is positive and the curvatureradius R2 is negative, i.e. a shape of a biconvex lens near the opticalaxis X.

The second lens L2 is formed in a shape of a meniscus lens so that acurvature radius of an object-side surface thereof R3 and a curvatureradius of an image plane-side surface thereof R4 are both positive anddirects a convex surface thereof to the object side near the opticalaxis X. In addition, as described above, the second lens L2 is formed tosatisfy the following conditional expressions (3) and (5). The secondlens L2 and the first lens L1 are lenses having strong refractive powersamong the lenses in the lens system. According to the embodiment, thefirst lens L1 and the second lens L2 satisfy the following conditionalexpression (4). When the imaging lens satisfies the conditionalexpression (4), it is possible to restrain Petzval sum of the whole lenssystem near zero and restrain an astigmatism, a field curvature, and achromatic aberration within preferred ranges in a well-balanced manner.

−1.8<f2/f<−0.8  (3)

−1.0<f1/f2<−0.4  (4)

1.5<R2f/R2r<6.0  (5)

In the above conditional expressions:

R2 f: Curvature radius of an object-side surface of the second lensR2 r: Curvature radius of an image plane-side surface of the second lens

In order to more satisfactorily correct aberrations, the imaging lenspreferably satisfies the following conditional expression (4A). Theimaging lenses in Numerical Data Examples 1 to 5 satisfy the followingconditional expression (4A):

−0.7<f1/f2<−0.4  (4A)

On the other hand, the third lens L3 is formed in a shape so that acurvature radius of an object-side surface thereof R5 is positive and acurvature radius of an image plane-side surface R6 is negative, so as tohave a shape of a biconvex lens near the optical axis X. Here, the shapeof the third lens L3 is not limited to a shape of a biconvex lens nearthe optical axis X and can be any as long as it is formed in a shape sothat the curvature radius of the object surface thereof R5 is positive.Numerical Data Examples 1 to 3 are examples in which the third lens L3has a shape of a biconvex lens near the optical axis X. Numerical DataExamples 4 and 5 are examples in which the third lens L3 has a shape ofa meniscus lens directing a convex surface thereof to the object sidenear the optical axis X.

The third lens L3 satisfies the following conditional expression (6).With this configuration, it is possible to more satisfactorily correctaberrations. The imaging lenses in Numerical Data Examples 1 to 5satisfy the following conditional expression (6):

5.0<f3/f<20.0  (6)

The fourth lens L4 is formed in a shape so that a curvature radius of anobject-side surface thereof R7 and a curvature radius of an imageplane-side surface thereof R8 are both negative, i.e. a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. As described above, the second lens L2 isformed in a shape of a meniscus lens directing a convex surface thereofto the object side near the optical axis X. Forming the fourth lens L4in a shape of a meniscus lens directing a concave surface thereof to theobject side near the optical axis X, the second lens L2 and the fourthlens L4 are arranged directing their concave surfaces to the third lensL3. Therefore, aberrations occurred in the first lens L1 are suitablycorrected by the negative-positive-negative refractive power arrangementof the lenses from the second lens L2 to the fourth lens L4 and theshapes of the respective lens surfaces of the second lens L2 and thefourth lens L4.

The third lens L3 and the fourth lens L4 mainly serve for correctingaberrations. According to the imaging lens of this embodiment,restraining the sag (sagittal height) of each lens surface of the thirdlens L3 and the fourth lens L4 within certain range, aberrations aresatisfactorily corrected. More specifically, when the maximum effectivediameter of the object-side surface of the third lens L3 is Φ_(3A), themaximum effective diameter of the image plane-side surface thereof isΦ_(3B), the maximum effective diameter of the object-side surface of thefourth lens L4 is Φ_(4A), the maximum effective diameter of the imageplane-side surface thereof is Φ_(4B), and the maximum absolute value ofa sag at up to 70% of the maximum effective diameters Φ_(3A) to Φ_(4B)is Z_(0.7), the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (7). Theimaging lenses of Numerical Data Examples 1 to 5 satisfy the conditionalexpression (7):

Z _(0.7) /f<0.1  (7)

With the maximum sags being restrained below the upper limit of theconditional expression (7), the third lens L3 and the fourth lens L4have substantially uniform thicknesses in a direction of the opticalaxis X, and thereby have less curved shapes. With such lens shapes,aberrations are more satisfactorily corrected. Furthermore, sensitivityto deterioration of the image-forming performance due to decentering(axial displacement), tilting, or the like upon manufacturing theimaging lens, i.e. so-called “production error sensitivity” decreases.In addition, because of the substantially uniform thickness in theoptical axis direction, fabrication properties upon production areimproved and manufacturing cost of the imaging lens can be restrained.Here, “sag” means, in each surface, a distance in a direction parallelto the optical axis X from a tangential plane that is orthogonal to theoptical axis X to the surface.

Here, each of lenses from the second lens L2 to the fourth lens L4satisfies the following conditional expressions (8) and (9). With thisconfiguration, aberrations are more satisfactorily corrected. Inaddition, since the maximum emitting angle of an off-axis light beam iskept small, generation of the shading phenomenon is restrained.

5.0<f34/f<25.0  (8)

0.3<dA/dB<1.5  (9)

In the above conditional expressions:

f34: Composite focal length of the third lens L3 and the fourth lens L4dA: Distance on an optical axis from an image plane-side surface of thesecond lens L2 to an object-side surface of the third lens L3dB: Distance on an optical axis from an image plane-side surface of thethird lens L3 to an object-side surface of the fourth lens L4

The fifth lens L5 is formed in a shape so that a curvature radius of anobject-side surface thereof R9 and a curvature radius of an imageplane-side surface thereof R10 are both positive, so as to have a shapeof a meniscus lens directing a convex surface thereof to the object sidenear the optical axis X. In addition, an image plane-side surface of thefifth lens L5 is formed as an aspheric shape so as to be convex to theobject side near the optical axis X and concave to the object side atthe periphery. With such shape of the fifth lens L5, it is possible tosuitably restrain an incident angle of a light beam emitted from theimaging lens to the image plane IM.

Here, it is not necessary to satisfy all of the conditional expressions(1) to (9) and (4A), and it is possible to obtain an effectcorresponding to the respective conditional expression when any singleone of the conditional expressions is individually satisfied.

In the embodiment, each lens has lens surfaces that are formed to be anaspheric surface. When the aspheric surfaces applied to the lenssurfaces have an axis Z in the optical axis direction, a height H in adirection perpendicular to the optical axis, a conical coefficient k,and aspheric coefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, and A₁₆, a shape ofthe aspheric surfaces of the lens surfaces may be expressed as follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, R represents a curvatureradius, d represents a distance between lens surfaces (surface spacing)on the optical axis, Nd represents a refractive index for a d line (areference wavelength in this embodiment), and νd represents the Abbe'snumber for the d line, respectively. Here, aspheric surfaces areindicated with surface numbers i affixed with * (asterisk).

Numerical Data Example 1

Basic lens data are shown below.

f = 3.75 mm, Fno = 2.4, ω = 34.2° Unit: mm Surface Data Surface Number iR d Nd νd (Object) ∞ ∞ 1* (Stop) 1.494 0.554 1.5346 56.0(=νd1) 2* 15.3070.055 3* 4.867(=R2f) 0.295 1.6354 23.9(=νd2) 4* 2.081(=R2r) 0.395(=dA)5* 199.951 0.443 1.5346 56.0(=νd3) 6* −13.687 0.479(=dB) 7* −5.445 0.3521.5346 56.0(=νd4) 8* −5.735 0.050 9* 1.429 0.690 1.5346 56.0(=νd5) 10* 1.179 0.230 11  ∞ 0.300 1.5163 64.1 12  ∞ 0.671 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −2.232E−03, A₆ = −4.156E−02,A₈ = 1.146E−01, A₁₀ = −1.020E−01 Second Surface k = 0.000, A₄ =−2.852E−01, A₆ = 7.759E−01, A₈ = −9.391E−01, A₁₀ = 3.755E−01 ThirdSurface k = 0.000, A₄ = −3.709E−01, A₆ = 1.044, A₈ = −1.322, A₁₀ =6.076E−01 Fourth Surface k = 0.000, A₄ = −1.733E−01, A₆ = 5.688E−01, A₈= −7.018E−01, A₁₀ = 3.827E−01 Fifth Surface k = 0.000, A₄ = −2.063E−01,A₆ = 1.702E−01, A₈ = −1.919E−01, A₁₀ = 1.962E−01, A₁₂ = −3.889E−02, A₁₄= −7.757E−02, A₁₆ = 7.712E−02 Sixth Surface k = 0.000, A₄ = −1.502E−01,A₆ = 7.633E−02, A₈ = −2.745E−01, A₁₀ = 4.997E−01, A₁₂ = −4.127E−01, A₁₄= 1.599E−01, A₁₆ = −1.374E−02 Seventh Surface k = 0.000, A₄ = 3.640E−01,A₆ = −4.621E−01, A₈ = 3.053E−01, A₁₀ = −1.135E−01, A₁₂ = −4.504E−03, A₁₄= 1.468E−02, A₁₆ = −2.511E−03 Eighth Surface k = 0.000, A₄ = 7.839E−02,A₆ = 3.330E−02, A₈ = −7.131E−02, A₁₀ = 3.114E−02, A₁₂ = −7.637E−03, A₁₄= 1.613E−03, A₁₆ = −2.096E−04 Ninth Surface k = −1.189, A₄ = −4.505E−01,A₆ = 2.283E−01, A₈ = −5.421E−02, A₁₀ = 2.224E−03, A₁₂ = 1.448E−03, A₁₄ =−1.660E−04, A₁₆ = −1.344E−05 Tenth Surface k = −2.993, A₄ = −2.108E−01,A₆ = 1.146E−01, A₈ = −4.590E−02, A₁₀ = 1.134E−02, A₁₂ = −1.666E−03, A₁₄= 1.401E−04, A₁₆ = −6.057E−06 f1 = 3.06 mm f2 = −5.97 mm f3 = 23.98 mmf4 = −349.61 mm f5 = −319.33 mm f34 = 26.31 mm Z_(0.7) = 0.064 mmThe values of the respective conditional expressions are as follows:

f2/f=−1.59

f1/f2=−0.51

R2f/R2r=2.34

f3/f=6.39

Z _(0.7) /f=0.017

f34/f=7.02

dA/dB=0.82

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. A distance on the optical axisfrom an object-side surface of the first lens L1 to an image plane IM(the thickness of the filter 10 is a length in air, which is hereinafterthe same) is 4.41 mm, and miniaturization of the imaging lens issuitably attained.

FIG. 2 shows the lateral aberration that corresponds to a ratio H ofeach image height to the maximum image height (hereinafter referred toas “image height ratio H”) in the imaging lens of Numerical Data Example1, which is divided into a tangential direction and sagittal direction(which is also the same in FIGS. 5, 8, 11, and 14). Furthermore, FIG. 3shows a spherical aberration (mm), an astigmatism (mm), and a distortion(%) of the imaging lens of Numerical Data Example 1, respectively. Inthe aberration diagrams, for the lateral aberration diagrams andspherical aberration diagrams, aberrations at each wavelength, i.e. a gline (435.84 nm), an F line (486.13 nm), an e line (546.07 nm), a d line(587.56 nm), and a C line (656.27 nm), are indicated. In the astigmatismdiagram, the aberrations on a sagittal image surface S and on atangential image surface T are respectively indicated (which are thesame in FIGS. 6, 9, 12, and 15). As shown in FIGS. 2 and 3, in theimaging lens of Numerical Data Example 1, the aberrations aresatisfactorily corrected.

Numerical Data Example 2

Basic lens data are shown below.

f = 3.77 mm, Fno = 2.4, ω = 34.1° Unit: mm Surface Data Surface Number iR d Nd νd (Object) ∞ ∞ 1* (Stop) 1.493 0.556 1.5346 56.0(=νd1) 2* 14.7840.056 3* 4.729(=R2f) 0.300 1.6142 25.6(=νd2) 4* 2.007(=R2r) 0.397(=dA)5* 108.743 0.421 1.5346 56.0(=νd3) 6* −14.924 0.476(=dB) 7* −5.091 0.3601.5346 56.0(=νd4) 8* −5.369 0.050 9* 1.418 0.698 1.5346 56.0(=νd5) 10* 1.165 0.230 11  ∞ 0.300 1.5163 64.1 12  ∞ 0.678 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.255E−03, A₆ = −4.129E−02,A₈ = 1.132E−01, A₁₀ = −1.049E−01 Second Surface k = 0.000, A₄ =−2.825E−01, A₆ = 7.723E−01, A₈ = −9.440E−01, A₁₀ = 3.726E−01 ThirdSurface k = 0.000, A₄ = −3.734E−01, A₆ = 1.044, A₈ = −1.323, A₁₀ =6.032E−01 Fourth Surface k = 0.000, A₄ = −1.717E−01, A₆ = 5.707E−01, A₈= −6.998E−01, A₁₀ = 3.844E−01 Fifth Surface k = 0.000, A₄ = −2.054E−01,A₆ = 1.713E−01, A₈ = −1.914E−01, A₁₀ = 1.958E−01, A₁₂ = −3.960E−02, A₁₄= −7.774E−02, A₁₆ = 7.858E−02 Sixth Surface k = 0.000, A₄ = −1.524E−01,A₆ = 7.643E−02, A₈ = −2.748E−01, A₁₀ = 4.993E−01, A₁₂ = −4.129E−01, A₁₄= 1.599E−01, A₁₆ = −1.368E−02 Seventh Surface k = 0.000, A₄ = 3.640E−01,A₆ = −4.616E−01, A₈ = 3.053E−01, A₁₀ = −1.136E−01, A₁₂ = −4.529E−03, A₁₄= 1.468E−02, A₁₆ = −2.504E−03 Eighth Surface k = 0.000, A₄ = 7.910E−02,A₆ = 3.361E−02, A₈ = −7.125E−02, A₁₀ = 3.114E−02, A₁₂ = −7.641E−03, A₁₄= 1.611E−03, A₁₆ = −2.105E−04 Ninth Surface k = −1.185, A₄ = −4.504E−01,A₆ = 2.282E−01, A₈ = −5.422E−02, A₁₀ = 2.221E−03, A₁₂ = 1.447E−03, A₁₄ =−1.663E−04, A₁₆ = −1.361E−05 Tenth Surface k = −3.044, A₄ = −2.102E−01,A₆ = 1.146E−01, A₈ = −4.589E−02, A₁₀ = 1.134E−02, A₁₂ = −1.666E−03, A₁₄= 1.401E−04, A₁₆ = −6.063E−06 f1 = 3.06 mm f2 = −5.92 mm f3 = 24.58 mmf4 = −334.74 mm f5 = −315.43 mm f34 = 27.16 mm Z_(0.7) = 0.063 mm

The values of the respective conditional expressions are as follows:

f2/f=−1.57

f1/f2=−0.52

R2f/R2r=2.36

f3/f=6.52

Z _(0.7) /f=0.017

f34/f=7.20

dA/dB=0.83

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. A distance on the optical axisfrom an object-side surface of the first lens L1 to the image plane IMis 4.42 mm, and miniaturization of the imaging lens is suitablyattained.

FIG. 5 shows the lateral aberration that corresponds to the image heightratio H, and FIG. 6 shows a spherical aberration (mm), an astigmatism(mm), and a distortion (%), respectively, in the imaging lens ofNumerical Data Example 2. As shown in FIGS. 5 and 6, also in the imaginglens of Numerical Data Example 2, the image surface is satisfactorilycorrected and the aberrations are suitably corrected similarly toNumerical Data Example 1.

Numerical Data Example 3

Basic lens data are shown below.

f = 3.75 mm, Fno = 2.4, ω = 33.7° Unit: mm Surface Data Surface Number iR d Nd νd (Object) ∞ ∞ 1* (Stop) 1.469 0.529 1.5346 56.0(=νd1) 2* 17.6040.057 3* 5.107(=R2f) 0.311 1.6142 25.6(=νd2) 4* 1.967(=R2r) 0.416(=dA)5* 17.450 0.397 1.5346 56.0(=νd3) 6* −30.875 0.475(=dB) 7* −4.948 0.3551.5346 56.0(=νd4) 8* −5.213 0.100 9* 1.293 0.600 1.5346 56.0(=νd5) 10* 1.078 0.230 11  ∞ 0.300 1.5163 64.1 12  ∞ 0.679 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −8.828E−03, A₆ = −3.600E−02,A₈ = 9.073E−02, A₁₀ = −1.009E−01 Second Surface k = 0.000, A₄ =−3.033E−01, A₆ = 7.653E−01, A₈ = −9.313E−01, A₁₀ = 4.154E−01 ThirdSurface k = 0.000, A₄ = −3.902E−01, A₆ = 1.046, A₈ = −1.308, A₁₀ =6.546E−01 Fourth Surface k = 0.000, A₄ = −1.685E−01, A₆ = 5.385E−01, A₈= −6.571E−01, A₁₀ = 3.751E−01 Fifth Surface k = 0.000, A₄ = −2.018E−01,A₆ = 1.608E−01, A₈ = −1.860E−01, A₁₀ = 1.964E−01, A₁₂ = −4.170E−02, A₁₄= −8.252E−02, A₁₆ = 7.450E−02 Sixth Surface k = 0.000, A₄ = −1.444E−01,A₆ = 7.709E−02, A₈ = −2.736E−01, A₁₀ = 5.001E−01, A₁₂ = −4.125E−01, A₁₄= 1.604E−01, A₁₆ = −1.293E−02 Seventh Surface k = 0.000, A₄ = 3.633E−01,A₆ = −4.604E−01, A₈ = 3.078E−01, A₁₀ = −1.143E−01, A₁₂ = −4.492E−03, A₁₄= 1.475E−02, A₁₆ = −2.511E−03 Eighth Surface k = 0.000, A₄ = 8.745E−02,A₆ = 3.309E−02, A₈ = −7.145E−02, A₁₀ = 3.112E−02, A₁₂ = −7.667E−03, A₁₄= 1.606E−03, A₁₆ = −2.108E−04 Ninth Surface k = −1.169, A₄ = −4.523E−01,A₆ = 2.282E−01, A₈ = −5.435E−02, A₁₀ = 2.186E−03, A₁₂ = 1.437E−03, A₁₄ =−1.637E−04, A₁₆ = −1.044E−05 Tenth Surface k = −3.124, A₄ = −2.106E−01,A₆ = 1.146E−01, A₈ = −4.588E−02, A₁₀ = 1.135E−02, A₁₂ = −1.663E−03, A₁₄= 1.403E−04, A₁₆ = −6.224E−06 f1 = 2.96 mm f2 = −5.41 mm f3 = 20.91 mmf4 = −338.97 mm f5 = −402.36 mm f34 = 22.82 mm Z_(0.7) = 0.050 mm

The values of the respective conditional expressions are as follows:

f2/f=−1.44

f1/f2=−0.55

R2f/R2r=2.60

f3/f=5.58

Z _(0.7) /f=0.013

f34/f=6.09

dA/dB=0.88

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. A distance on the optical axisfrom an object-side surface of the first lens L1 to the image plane IMis 4.35 mm, and miniaturization of the imaging lens is suitablyattained.

FIG. 8 shows the lateral aberration that corresponds to the image heightratio H, and FIG. 9 shows a spherical aberration (mm), an astigmatism(mm), and a distortion (%), respectively, in the imaging lens ofNumerical Data Example 3. As shown in FIGS. 8 and 9, also in the imaginglens of Numerical Data Example 3, the image surface is satisfactorilycorrected and the aberrations are suitably corrected similarly toNumerical Data Example 1.

Numerical Data Example 4

Basic lens data are shown below.

f = 3.85 mm, Fno = 2.4, ω = 33.0° Unit: mm Surface Data Surface Number iR d Nd νd (Object) ∞ ∞ 1* (Stop) 1.496 0.563 1.5346 56.0(=νd1) 2* 11.0520.054 3* 4.359(=R2f) 0.318 1.6354 23.9(=νd2) 4* 2.129(=R2r) 0.403(=dA)5* 25.104 0.428 1.5346 56.0(=νd3) 6* 100.397 0.488(=dB) 7* −5.675 0.3571.5346 56.0(=νd4) 8* −5.990 0.050 9* 1.432 0.706 1.5346 56.0(=νd5) 10* 1.176 0.230 11  ∞ 0.300 1.5163 64.1 12  ∞ 0.655 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −2.168E−03, A₆ = −4.526E−02,A₈ = 1.120E−01, A₁₀ = −1.002E−01 Second Surface k = 0.000, A₄ =−2.877E−01, A₆ = 7.705E−01, A₈ = −9.423E−01, A₁₀ = 3.788E−01 ThirdSurface k = 0.000, A₄ = −3.725E−01, A₆ = 1.047, A₈ = −1.321, A₁₀ =6.019E−01 Fourth Surface k = 0.000, A₄ = −1.760E−01, A₆ = 5.612E−01, A₈= −7.063E−01, A₁₀ = 3.859E−01 Fifth Surface k = 0.000, A₄ = −2.054E−01,A₆ = 1.634E−01, A₈ = −1.966E−01, A₁₀ = 1.934E−01, A₁₂ = −4.027E−02, A₁₄= −7.780E−02, A₁₆ = 7.807E−02 Sixth Surface k = 0.000, A₄ = −1.488E−01,A₆ = 8.112E−02, A₈ = −2.722E−01, A₁₀ = 5.006E−01, A₁₂ = −4.126E−01, A₁₄= 1.597E−01, A₁₆ = −1.423E−02 Seventh Surface k = 0.000, A₄ = 3.653E−01,A₆ = −4.620E−01, A₈ = 3.053E−01, A₁₀ = −1.135E−01, A₁₂ = −4.476E−03, A₁₄= 1.471E−02, A₁₆ = −2.496E−03 Eighth Surface k = 0.000, A₄ = 7.807E−02,A₆ = 3.337E−02, A₈ = −7.124E−02, A₁₀ = 3.117E−02, A₁₂ = −7.628E−03, A₁₄= 1.616E−03, A₁₆ = −2.088E−04 Ninth Surface k = −1.190, A₄ = −4.506E−01,A₆ = 2.282E−01, A₈ = −5.418E−02, A₁₀ = 2.248E−03, A₁₂ = 1.456E−03, A₁₄ =−1.640E−04, A₁₆ = −1.308E−05 Tenth Surface k = −3.033, A₄ = −2.109E−01,A₆ = 1.145E−01, A₈ = −4.591E−02, A₁₀ = 1.134E−02, A₁₂ = −1.665E−03, A₁₄= 1.403E−04, A₁₆ = −6.039E−06 f1 = 3.17 mm f2 = −6.93 mm f3 = 62.49 mmf4 = −334.24 mm f5 = −311.61 mm f34 = 78.62 mm Z_(0.7) = 0.039 mm

The values of the respective conditional expressions are as follows:

f2/f=−1.80

f1/f2=−0.46

R2f/R2r=2.05

f3/f=16.23

Z _(0.7) /f=0.010

f34/f=20.42

dA/dB=0.83

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. A distance on the optical axisfrom an object-side surface of the first lens L1 to the image plane IMis 4.45 mm, and miniaturization of the imaging lens is suitablyattained.

FIG. 11 shows the lateral aberration that corresponds to the imageheight ratio H, and FIG. 12 shows a spherical aberration (mm), anastigmatism (mm), and a distortion (%), respectively, in the imaginglens of Numerical Data Example 4. As shown in FIGS. 11 and 12, also inthe imaging lens of Numerical Data Example 4, the image surface issatisfactorily corrected and the aberrations are suitably correctedsimilarly to Numerical Data Example 1.

Numerical Data Example 5

Basic lens data are shown below.

f = 4.03 mm, Fno = 2.4, ω = 33.8° Unit: mm Surface Data Surface Number iR d Nd νd (Object) ∞ ∞ 1* (Stop) 1.435 0.582 1.5346 56.0(=νd1) 2* 19.3990.050 3* 12.591(=R2f) 0.300 1.6142 25.6(=νd2) 4*  2.327(=R2r) 0.427(=dA)5* 2.533 0.317 1.5346 56.0(=νd3) 6* 2.867 0.496(=dB) 7* −4.253 0.3951.5346 56.0(=νd4) 8* −4.460 0.050 9* 1.465 0.683 1.5346 56.0(=νd5) 10* 1.176 0.230 11  ∞ 0.300 1.5163 64.1 12  ∞ 0.758 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.069E−02, A₆ = −3.135E−02,A₈ = 6.640E−02, A₁₀ = −7.875E−02 Second Surface k = 0.000, A₄ =−2.936E−01, A₆ = 7.790E−01, A₈ = −8.988E−01, A₁₀ = 3.456E−01 ThirdSurface k = 0.000, A₄ = −3.251E−01, A₆ = 1.044, A₈ = −1.254, A₁₀ =5.701E−01 Fourth Surface k = 0.000, A₄ = −1.182E−01, A₆ = 5.603E−01, A₈= −6.761E−01, A₁₀ = 3.725E−01 Fifth Surface k = 0.000, A₄ = −2.166E−01,A₆ = 1.845E−01, A₈ = −2.115E−01, A₁₀ = 2.047E−01, A₁₂ = −5.521E−02, A₁₄= −9.370E−02, A₁₆ = 5.066E−02 Sixth Surface k = 0.000, A₄ = −1.396E−01,A₆ = 9.119E−02, A₈ = −2.877E−01, A₁₀ = 5.054E−01, A₁₂ = −4.175E−01, A₁₄= 1.590E−01, A₁₆ = −2.205E−02 Seventh Surface k = 0.000, A₄ = 3.837E−01,A₆ = −4.522E−01, A₈ = 2.893E−01, A₁₀ = −1.088E−01, A₁₂ = −2.938E−03, A₁₄= 1.541E−02, A₁₆ = −3.082E−03 Eighth Surface k = 0.000, A₄ = 6.462E−02,A₆ = 4.386E−02, A₈ = −7.139E−02, A₁₀ = 3.095E−02, A₁₂ = −7.683E−03, A₁₄= 1.586E−03, A₁₆ = −1.918E−04 Ninth Surface k = −1.584, A₄ = −4.420E−01,A₆ = 2.332E−01, A₈ = −5.365E−02, A₁₀ = 1.387E−03, A₁₂ = 1.454E−03, A₁₄ =−1.265E−04, A₁₆ = −1.213E−05 Tenth Surface k = −3.311, A₄ = −2.134E−01,A₆ = 1.163E−01, A₈ = −4.577E−02, A₁₀ = 1.136E−02, A₁₂ = −1.717E−03, A₁₄= 1.438E−04, A₁₆ = −5.312E−06 f1 = 2.87 mm f2 = −4.70 mm f3 = 30.60 mmf4 = −515.28 mm f5 = −411.21 mm f34 = 33.51 mm Z_(0.7) = 0.066 mm

The values of the respective conditional expressions are as follows:

f2/f=−1.17

f1/f2=−0.61

R2f/R2r=5.41

f3/f=7.59

Z _(0.7) /f=0.016

f34/f=8.32

dA/dB=0.86

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. A distance on the optical axisfrom an object-side surface of the first lens L1 to the image plane IMis 4.49 mm, and miniaturization of the imaging lens is suitablyattained.

FIG. 14 shows the lateral aberration that corresponds to the imageheight ratio H, and FIG. 15 shows a spherical aberration (mm), anastigmatism (mm), and a distortion (%), respectively, in the imaginglens of Numerical Data Example 5. As shown in FIGS. 14 and 15, also inthe imaging lens of Numerical Data Example 5, the image surface issatisfactorily corrected and the aberrations are suitably correctedsimilarly to Numerical Data Example 1.

Accordingly, when the imaging lens of the embodiment is applied to animaging optical system of a cellular phone, a digital still camera, aportable information terminal, a security camera, a vehicle onboardcamera, a network camera, and the like, it is possible to achieve boththe high performance and the small size for the camera or the like.

Here, the imaging lens of the invention is not limited to theabove-described embodiment. In the above-described embodiment, anysurfaces of the first lens L1 through the fifth lens L5 are formed asaspheric surfaces, but it is not necessary to form all the surfaces asaspheric surfaces. Alternatively, it is also possible to form one of orboth surfaces of any lens from the first lens L1 through the fifth lensin a spherical surface(s).

The invention may be applicable to the imaging lens of a device that isrequired to have a small size and satisfactory aberration correctionability, e.g., the imaging lenses used in the cellular phones, thedigital still cameras, and the like.

The disclosure of Japanese Patent Application No. 2011-190560, filed onSep. 1, 2011, is incorporated in the application.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingpositive refractive power; a second lens; a third lens; a fourth lens;and a fifth lens having negative refractive power, arranged in thisorder from an object side to an image plane side, wherein said firstlens is formed in a shape so that a curvature radius of a surfacethereof on the object side is positive, said second lens is formed in ashape so that a curvature radius of a surface thereof on the object sideand a curvature radius of a surface thereof on the image plane side areboth positive, each of said first lens and said third lens has an Abbe'snumber greater than 45, said second lens has an Abbe's number less than35, said third lens has a focal length f3 so that the followingconditional expression is satisfied:5.58≦|f3|/f≦16.23 where f is a focal length of a whole lens system, saidsecond lens and said third lens are arranged so that the surface of thesecond lens on the image plane side is situated away from a surface ofthe third lens on the object side by a distance dA on an optical axis,and said third lens and said fourth lens are arranged so that a surfaceof the third lens on the image plane side is situated away from asurface of the fourth lens on the object side by a distance dB on theoptical axis so that the following conditional expression is satisfied:0.3<dA/dB<1.5.
 2. The imaging lens according to claim 1, wherein saidsecond lens has negative refractive power, said third lens has positiverefractive power, and said fourth lens has negative refractive power. 3.The imaging lens according to claim 1, wherein said third lens is formedin a shape so that a curvature radius of a surface thereof on the objectside is positive, and said fifth lens is formed in a shape so that acurvature radius of a surface thereof on the object side and a curvatureradius of a surface thereof on the image plane side are both positive.4. The imaging lens according to claim 1, wherein each of said fourthlens and said fifth lens has an Abbe's number greater than
 45. 5. Theimaging lens according to claim 1, wherein said fourth lens is formed ina shape so that a curvature radius of the surface thereof on the objectside and a curvature radius of a surface thereof on the image plane sideare both negative.
 6. The imaging lens according to claim 1, whereinsaid second lens has a focal length f2 so that the following conditionalexpression is satisfied:−1.8<f2/f<−0.8.
 7. The imaging lens according to claim 1, wherein saidfirst lens has a focal length f1, and said second lens has a focallength f2 so that the following conditional expression is satisfied:−1.0<f1/f2<−0.4.
 8. The imaging lens according to claim 1, wherein saidsecond lens is formed in the shape so that the surface thereof on theobject side has the curvature radius R2 f and the surface thereof on theimage plane side has the curvature radius R2 r so that the followingconditional expression is satisfied:1.5<R2f/R2r<6.0.
 9. The imaging lens according to claim 1, wherein saidsecond lens has a focal length f2, and said fifth lens has a focallength f5 so that the following conditional expressions are satisfied:|f2|<f3 and |f2|<|f5|.
 10. The imaging lens according to claim 1,wherein said first lens has a focal length f1, and said fourth lens hasa focal length f4 so that the following conditional expressions aresatisfied:f1<f3 and f3<|f4|.
 11. An imaging lens comprising: a first lens havingpositive refractive power; a second lens; a third lens having positiverefractive power; a fourth lens; and a fifth lens, arranged in thisorder from an object side to an image plane side, wherein said firstlens is formed in a shape so that a curvature radius of a surfacethereof on the object side and a curvature radius of a surface thereofon the image plane side are both positive, said second lens is formed ina shape so that a surface thereof on the image plane side is aspherical,and a curvature radius of a surface thereof on the object side and acurvature radius of the surface thereof on the image plane side are bothpositive, said third lens is formed in a shape so that at least one of asurface thereof on the object side and a surface thereof on the imageplane side is aspherical, said fourth lens is formed in a shape so thata surface thereof on the object side and a surface thereof on the imageplane side are aspherical, and a curvature radius of the surface thereofon the image plane side is negative, said fifth lens is formed in ashape so that a surface thereof on the object side and a surface thereofon the image plane side are aspherical, said second lens has a focallength f2, said third lens has a focal length f3, said fourth lens has afocal length f4, and said fifth lens has a focal length f5 so that thefollowing conditional expressions are satisfied:f3<|f4| and |f2|<|f5|.
 12. The imaging lens according to claim 11,wherein said second lens has negative refractive power, said fourth lenshas negative refractive power, and said fifth lens has negativerefractive power.
 13. The imaging lens according to claim 11, whereinsaid third lens is formed in a shape so that a curvature radius of thesurface thereof on the object side is positive, and said fifth lens isformed in a shape so that a curvature radius of the surface thereof onthe object side and a curvature radius of the surface thereof on theimage plane side are both positive.
 14. The imaging lens according toclaim 11, wherein each of said first lens, said third lens, said fourthlens, and said fifth lens has an Abbe's number greater than 45, and saidsecond lens has an Abbe's number less than
 35. 15. The imaging lensaccording to claim 11, wherein said first lens has a focal length f1 sothat the following conditional expressions are satisfied:f1<f3 and |f2|<f3.
 16. The imaging lens according to claim 11, whereinsaid second lens has the focal length f2 so that the followingconditional expression is satisfied:−1.8<f2/f<−0.8 where f is a focal length of a whole lens system.
 17. Theimaging lens according to claim 11, wherein said first lens has a focallength f1 so that the following conditional expression is satisfied:−1.0<f1/f2<−0.4.
 18. The imaging lens according to claim 11, whereinsaid second lens is formed in the shape so that the surface thereof onthe object side has the curvature radius R2 f and the surface thereof onthe image plane side has the curvature radius R2 r so that the followingconditional expression is satisfied:1.5<R2f/R2r<6.0.
 19. The imaging lens according to claim 11, whereinsaid second lens and said third lens are arranged so that the surface ofthe second lens on the image plane side is situated away from thesurface of the third lens on the object side by a distance dA on anoptical axis, and said third lens and said fourth lens are arranged sothat the surface of the third lens on the image plane side is situatedaway from the surface of the fourth lens on the object side by adistance dB on the optical axis so that the following conditionalexpression is satisfied:0.3<dA/dB<1.5.
 20. The imaging lens according to claim 11, wherein saidthird lens has the focal length f3 so that the following conditionalexpression is satisfied:5.0<f3/f<20.0 where f is a focal length of a whole lens system.